Zinc base die-casting alloy



Patented Oct. 1930 a uuirao sra PA ENT o l-rice EDMUND L, 'aNnrmsoN, or ramnnroN, rnNNsynvaNm, assreNon are THE. JERSEY ZINC comm, or New York, N. 2., a oonrona-rxoN or New my zINc Basia nmoasrme ALLOY No Drawing. 1 I

This invention relates to ainc base dieimproved and superior the die:

casting operation necessitate the construction of the melting pot and die'from iron and steel. These metals are subject to attack by molten zinc and it has been found from ex-1 perience, to minimize this; attack sufliciently to secure reasonable life from the machines,

that at least 0.25% aluminum must be addedto the zinc. Alloys for die-casting must possess a sufficient degree of fluidity to properly flow into and completely fill the dies used, and 2% or more aluminum appears to be necessary to secure an adequate degree of fluidity. It has also longbeen known that aluminum increases the tensile strength of zinc and this, in itself, makes its presence.

in zinc base 'die-casting alloys desirable in quantities of from 2% to as much as 10 to 15%. a Zinc-aluminum alloys containing less than about 80% of aluminum undergo a structural change subsequent to solidificationwhich is commonly known as a phase change orimore specifically in this case as an eutectoi'd reaction. formation 'of two crystalline forms or phases fromonephase previously'existing, and is accompanied by certain chan es in physical properties of the alloy, such, or example, as increase in density, hardness and tensile strength and decrease in ductility and impact strength. Thisphase change may occur during the'cooling of the alloy after casting or may through or inhibite In such cases it may take place gradually over a period of months at ordiproase

This phase change consists in the.

certaininfluences bev retarded Application filed June 5, 1929. Serial No. 368,730.

sometimes occurs is the growth or coalescence of'the extreme small particles of the new phases as first ormed into largerparticlw' This stage may be accompanied by softening and lowering of tensile strength and by an increase in ductility and-impact strength.

Zinc-aluminum alloys in this range of com- 7 position are alsosubject to a of'disintegrationcommonly known as intercrystalline oxidation. In extreme cases, under the influence of warmth and moisture, intercrystalline oxidation ma completely penetrate specimens of these oys and cause swelling, warping and even complete disintegration.

Intercrystalline oxidation is in some way associated with and partly dependent upon the phase change.

- It has heretofore been recognized that 'cer- I tain other metals when present in these zincaluminum alloys exercise important effects on either the phase change or the intercrystaL- line oxidation or both. For example, copper and-magnesium are known to exert an mfluence on the phase change either in V to' the rate at which it takes place or the completeness of the reaction orin some other 7 respect not fully understood; .The particular efiect produced by copper and magnesium on respect the phase change reacts favorably in increasing the resistance of the alloys to intefcrystalline' oxidation. Lead, while not exerting any marked influence. on the phase change,

veryseriously diminishes theresistanoe of i these zinc-aluminum alloys to intercrystalline oxidation. Cadmium though having a oer-*- tain effect on the phase change, in the presonce of lead also diminishes the'res'istan cjeofthese alloys to intercrystalline oxidation.

Zinc base alloys suitable ior die-casting are 1 km and in em aluminum, 3%copper and the balance high grade zinc metal is widely used and is 314 31,. .factory for many purposes; allgy is, ve be n to w j tions: ir'st;

upon aging, "either at temperatures or at slightly elevated temperatures, the alin the presence of warmth and moisture together, the alloy undergoes intercrystalline oxidation which causes serious changes in physical properties and dimensions.

An improved zinc base alloy for die-casting is described in the United States patent of Peirce and Anderson, No. 1,596,761, dated August 17, 1926. This alloy (which, as marketed, is usually of the composition 4% aluminum, 3% copper, 0.1% magnesium and the balance high grade zinc) is virtually free from the second fault of the first mentioned alloy, namely, intercrystalline oxidation.

It is, however, subject to the first fault, namely, loss of impact strength and change of dimensions upon aging. This objectionable property of these alloys prevents their use in a wide field of" otherwise suitable applications. These alloys have a Very high tensile strength much beyond that ordinarily needed and the elimination of the faults just described even at the expense of a considerable reduction intensile strength would be advantageous.

I have discovered that copper (which is present in the foregoing alloys principally to aid in preventing intercrystalline oxidation) is responsible for the loss of impact strength and change in dimensions upon aging, and that an alloy virtually free from o jectionabl'e aging changes can be produced from high grade zinc metal by the addition of 4% of aluminum and 0.1% magnesium. This alloy also possesses the other properties requisite in a die-casting alloy. This alloy,

when made from high grade zinc metal containing as much as 0.06%' of lead plus cadmium, is subject to a certain degree of intercrystalline oxidation which, to some extent, limits its use. I have discovered, however, that by reducing the lead plus cadmium content materially, an alloy of the above com-- position can be produced which is free from intercrystalline oxidation as well as. from aging changes .and which will therefore be suitable for a wide range of applications where the two known alloys previously discussed are not satisfactory. Such freedom from intercrystalline oxidation can be secured, for example, by the use of a grade of zinc metal containing 0.01% or less of lead plus cadmium.

- Based on these discoveries, my present invention resides in the provision of an improved zinc base die-casting alloy containing an appropriate amount of aluminum for die-casting purposes, say 2 to 15% (prefer.-

- ably about 4%), from 0.01 to 0.3% magnesium (preferably about 0.1%), and the balance high grade zinc metal (preferably containing at least 99.94% zinc). More particularly, the invention involves the provision of an improved zinc base die-casting alloy containing from 2 to 15% aluminum (preferably not morethan 5%), from 0.01 to 0.3% magnesium and in which the zinc base is zinc metal of high purity containing not more than 0.01% of lead plus cadmium and not more than 0.001% tin. In addition, the invention contemplates the provision of a die-casting made of a zinc base alloy and characterized by an impact strength that is not substantially impaired or decreased upon aging at normal or slightly elevated temperatures, and further characterized by a substantially negligible change in linear dimensions upon aging.

It has heretofore been recognized that superior results are usually obtained by employing high grade zin'c metal as the zinc base in the known die-casting alloys. The -well-known Horsehead brand zinc metal has been considered eminently satisfactory for the purpose, and it has not been considered necessary or advantageous to use zinc metal of higher purity. The Horsehead brand zinc metal averages 99.94% zinc and contains about 0.045% lead and about 0.003% cadmium.

In its preferred form, the improved zinc base die-casting alloy of the invention is made of a zinmmetal base of high purity containing not more than 0.01% lead plus cadmium. Very satisfactory results have been secured with zinc metal containing 9999+ zinc, less than-0.003% lead, less than 0.003% cadmium and less than 0.001% tin. Preferably, the zinc base alloy of the invention contains about 4% aluminum, about 0.1% magnesium and the balance zinc metal of high purity containing 9999+ ,zinc. Tin should be substantially excluded from the alloy, and in no case should the tin content exceed about 0.001%.

The following tables illustrate the improved physical properties of die-castings made of the alloy of the invention, more particularly the increase in impact stren h (Table II) and the substantially negligi 1e.

linear expansion (Table III) upon aging. Table IV shows the. increase in impact strengthand decrease in tensile strength occurring upon simple aging at elevated temperatures (without intercrystalline; oxidation or other corrosion). This change is presumably due to some particle growth following the phase chan e which was presumably completed during t e cooling following casting. Allo A is the preferred composition described in U. S. Patent No. 1,596,761 and alloy D is thepreferred composition of the alloy of the'present invention. In alloy B the zinc base is zinc metal of high purity instead of highgrade zinc metal (Horseh'ead brand) instead of zinc metal of high purity used in alloy D. In alloys A and C, the zinc metal base contained 9994+ zinc, while in alloys B and D the zinc metal base contained 99.99+% zinc.

Composition of alloys Zinc metal containing- Alloy Al Cu Mg Pb Cd Per cent Per cent Per cent Per cent Per cent I. Ultimate tensile strength in lbs. per sq. in. (flat tensile specimens) I After exposure to steam at 95 C. Afte 36 days ex- Alloy tposture 0 S 63111 As cast 1 day 5 days 10 days 20 days at A 45, 100 43, 600 32, 000 24, 900 20, 900 35, 000 B 46, 800 44, 100 43, 300 43, 000 38, 600 42, 100 C 37, 400 27, 900 18, 800 17, 100 D 41,800 36, 300. 33, 600 31, 900 29, 400 32, 800

II. Impact strength in ft'. lbs. per sq. inch After exposure to steam at 95 C. Afte 30 days ex- Alloy posure.

As cast 1 day 5 days 10 days 20 days 2% $33 105 46 9 7 e 13 130 94 34 17 13 23 109 85 20 14 8 87 109 9s 95 n9 III. Linear expansion in inches 6 After exposure to steam at 95 C. Aft 30 days ex- Alloy. posure As cast 1 day 5 days 10 days 20 days 2% $33 6 IV. Aging at elevated temperature in dry air Expan- Flat tensile Impact sion Alloy i l 10 days 10 days 10 days 9191511181 at 95 0. Ongmal at 95 0. at 95 0.

A 44, 900 42, 000 107 21 0. 0010 D 41, 800 33, 700 p 87 116 0. 00000 As will be seen from the foregoing tables,

' the improved alloy of the invention exhibits use of such die-castings wherever high grade zinc metal itself is not aifected by corroding influences. In addition to the properties illustrated by the tables, die-castings made of the improved alloy of the invention, after accelerated aging for 5 days in steam at 95 0., will Withstand a slow bend of about 30 before breaking. Die-castings made of the heretofore available zinc base alloys with whcih I have worked are capable, after similar'aging, of withstanding a slow bend of only about 5 or less. This slow bend test is a measure of the ability of the die-casting to withstand deformation.

I claim:

1. An alloy consisting of 2 to 5% aluminum, 0.01 to 0.3% magnesium and the balance high grade zinc metal.

2. An alloy consisting of approximately 4% aluminum, 0.1% magnesium and the balance high grade zinc.

3. An alloy consisting of 2 to 5% aluminum, 0.01 to 023% magnesium and the balance high purity containing not more than 0.003% I aluminum, about 0.1% magnesium and in which the zinc base is zinc metal of high purity containing not more than 0.01% of lead plus cadmium.

9. A zinc base alloy containing about 4% aluminum, about 0.1% I magnesium and in which the zinc base is zinc metal containing 9999+ zinc and not more than 0.003% lead and notmore than 0.003% cadmium and not more than 0.001% tin.

10. A zinc base alloy containing about 4% aluminum, about 0.1% magnesium and in which the zinc baseis zinc metal containin 99.99+'% zinc and lessthan 0.01% of lead plus cadmium. f

In testimony whereof I afiix my signature.

EDMUND A. ANDERSON. 

